The present invention relates to a method of transferring a device for selectively releasing a minutely processed device and transferring the device onto another substrate, a method of producing a device holding substrate, and a device holding substrate.
In the case of assembling an image display device by arranging light-emitting devices in a matrix, the devices are either included on a substrate as in liquid crystal display devices (LCDs) or plasma display panels (PDPs), or singular light-emitting diode (LED) packages are arranged as in light-emitting diode displays (LED displays). In an image display device such as an LCD and a PDP, separation of the devices is impossible with respect to the pitch of the devices or pixels and the production process thereof. Also, the devices are ordinarily spaced from each other by the pixel pitch of the image display device from the beginning of the production process which makes separation impossible.
Not limited to the light-emitting devices, there are semiconductor thin film devices or high density semiconductor devices included on a substrate and used to transfer the devices onto another substrate. For example, in a method for transferring a thin film device disclosed in Japanese Patent Laid-open No. Hei 11-26733, a substrate is used at the time of producing thin-film devices into liquid crystal control devices. This substrate is different from a substrate that is used at the time of mounting the product, where the thin-film devices are transferred onto the substrate used at the time of mounting. Another known transfer technique, for example, is the transferring method disclosed in Japanese Patent Laid-open No. Hei 7-254690. In this patent, a film capable of generating minute bubbles is included at the boundary portion between a substrate and a device (semiconductor plate). The film is irradiated with a laser beam to generate the minute bubbles when the device (semiconductor plate) is transferred to the side of a support. Furthermore, according to the technique disclosed in Japanese Patent Laid-open No. Hei 11-142878, thin-film transistors including a liquid crystal display portion on a first substrate are transferred entirely onto a second substrate, and then selectively transferred from the second substrate onto a third substrate corresponding to the pixel pitch.
However, the transfer techniques as mentioned above have the following problems. First, in the method of transferring a thin-film device disclosed in Japanese Patent Laid-open No. Hei 11-26733, a thermo-melting adhesive layer of a second separation layer undergoes ablation upon irradiation with laser light, and also generates a gas or the like, where the treatment of the gas or the like is a problem on a process basis. In addition, a portion of the thermo-melting adhesive layer is left on the device after the device is transferred onto a secondary transfer body. As a result, the adhesive layer residue must be removed using xylene or a similar solvent. Also, to adhere the device to the secondary transfer body an adhesive layer such as an epoxy resin is cured. A substantial period of time is required to cure the epoxy resin. Furthermore, in order to release the thin-film devices such as thin-film transistors from the entire substrate, amorphous silicon must be preliminarily provided on the whole surface of the substrate, and the whole surface must be irradiated with laser light.
In the transferring method disclosed in Japanese Patent Laid-open No. Hei 7-254690, only a laser light is transmitted through the transparent portions of the support body, so that only the transparent portions of the body enable the laser light to pass through the body. In addition, this patent describes that sufficient binding energy is provided between the semiconductor plate and the support body to promote adhesion between the support body and the semiconductor plate. However, the absorption of laser light occurs between the semiconductor plate and the support body, so that bubbles are generated by ablation to break the semiconductor devices, resulting in a decrease of yield.
In the technique disclosed in Japanese Patent Laid-open No. Hei 11-142878, the portions of the thin-film transistor devices to be transferred are selectively irradiated with UV light to lower the adhesive power of a UV release resin provided between the thin-film transistors and the substrate from which the transistors are to be transferred. However, it takes time for the adhesive power of the UV release resin to be lowered by irradiation with UV light, which leads to the lowering of throughput on a process basis. In addition, when the adhesive power is not sufficiently lowered, the transfer is also lowered.
Accordingly, it is an object of the present invention to provide a method of transferring a device, a method of producing a device holding substrate, and a device holding substrate which enable minutely processed devices to be transferred in a short time without inducing an increase in the number of steps and without lowering the yield of transfer.